1. Field of the Invention
This invention relates to the drilling of well bores into the earth, and more particularly, it relates to a well tool or jar interconnected into the string of well pipe for selectively delivering impacts thereto.
2. Description of Prior Art
Rotary drilling for making a well bore into the earth for the production of oil and gas has been practiced since the early 1900's, and many advantages of such drilling procedure have been appreciated. For this purpose, a well drill string is used and it usually includes a drill bit, drill collars and bore stabilizers, and a plurality of lengths of drill pipe secured to a kelly at the derrick which is situated on the earth's surface above the well bore. The kelly is a non-round, elongated piece of high strength steel that passes through a drive table on a derrick floor and connects to the top of the well drill string. The drive table rotates the drill string through the kelly and by this means, the drilling of the well bore is accomplished. A longitudinal passageway axially through the drill string, provides for the circulation of drilling fluid, commonly termed "mud." The mud passes downwardly in the well drill string, through the drill bit and then upwardly in the surrounding annulus for removing the drill cuttings from the well bore to the earth's surface. For example, a well bore of about 8 inches will require the use of an 85/8 inch drill bit, several 8 inch collars and stabilizers which are connected to the kelly through a suitable drill pipe, which may be for example 41/2 inches in diameter. In a medium depth well of 15,000 feet, the weight of the drill string, while partially supported by the drilling fluid, is in the neighborhood of about 200,000 pounds. The drilling fluid passes through the well drill string at pressures which can reach 2,500 psi but usually are in a range of about 1,500 during the drilling of a well bore not suffering from any serious problems of penetrating difficult-to-drill formations. The drive table must exert large levels of torque to rotate the well drilling string at the usual rates which may be between 35 to 60 RPM. Although the components of the well drill string appear to be massive and of great strength when viewed at the earth's surface, the drill string in such a moderately deep well, is in reality a highly flexible and relatively easy to damage drilling tool. For example, the drive table may be connected to a power source which can be of a magnitude of 3,000 horsepower. This primeover can apply at the drive table torque levels above 75,000 foot/pounds to rotate the drill string.
Under these conditions, the drill string in even a slightly curved well bore is severely laterally flexed at each revolution while the drilling of the well bore is undertaken. In frequent instances, this repeated flexing can cause injury to even a steel drill pipe.
For example, the bit may deviate from a desired vertical axis, and bore what might be termed a "crooked" hole. In such instances, the large diameter collars and other adjacent drill string components can become lodged in such dog-leg type well bores. If excessive torque is applied to the drill string under these lateral flexing conditions, the pin and box joints interconnecting the drill string or even the drill pipe itself can be torn in two parts. Thus, excessive torque to release the well drill string when it becomes "stuck" in a well bore are to be avoided.
It is common practice in the drilling of well bores to employ a specialized tool in the drill string at its lower end but above tools such as drill collars, reamers, stabilizers, etc., which have a greater diameter than that of the drill pipe. This tool is known in the oil patch as a drilling jar. The jar is a tool which can be placed in a latched condition and then either tension or weight loading applied to the drill pipe. The jar is selectively released and its components telescoped over a fixed dimension, which may be 8 inches, until hammer and anvil parts on the tool engage to deliver an exceedingly large impact or "jar" to the drill string. This type of hammering action, either upwardly or downwardly, will usually release the stuck portions of the well drill string from the well bore.
One jar that has met with universal, world wide acceptance and has been producing good results for many years is availabe commercially under the name "LI Rotary Drilling Jar." The structure and operation of this jar is clearly described in U.S. Pat. Nos. 3,208,541 and 3,233,690, both patents being issued to Mr. Richard R. Lawrence. This drilling jar, of the mechanical type, is capable of delivering adjustably impacts upon the drill string, selectively applied either upwardly or downwardly. These impacts can have maximum values in a 41/8 inch drill string of about 250,000 foot/pounds and in a 73/4 inch drill string about 770,805 foot/pounds. This rotary drilling jar is capable of repeatedly applying impacts to the well drill string for extended periods of time, as for example, several days in duration. The drilling jar is usually employed in every drill string as an insurance measure to prevent expensive, time consuming and difficult fishing operations to remove stuck portions of a drill string within a well bore.
The rotary drilling jar, of the type described above, must operate in a drilling fluid which contains sand, small particles of formation debris, and sometimes even pieces of metal which are torn from the drill string during the production of the well bore. Conventional rotary drilling jars all employ two telescoping parts which can move together or apart from one another in delivering upward or downward impacts, respectively. The latching mechanism in the jar is usually contained within a sealed and oil-filled chamber. As a result, fluid seals insure a fluid tight sliding interconnecting between the two telescoping parts. Obviously, one end of the annulus between the telescoping parts is exposed to the fluids within the well bore that surround the drilling jar. The well drill string including the jar suffers severe lateral flexing during the drilling of the well bore. Flexing of the jar produces compound longitudinal and axial forces on the fluid seals that can cause them to leak well fluid into the oil-filled latching chamber.
It will be apparent also that the impact delivered by the hammer and anvil surfaces of the jar produce a very substantial vibration effect. This vibration effect can cause injury to the fluid seals and permit the entry of undesired well fluid into the oil filled chamber carring the cocking and releasing mechanism of the rotary drilling jar. In the LI Drilling Jar and as shown in U.S. Pat. No. 3,233,690, one or more annular resilient rings are carried on the external telescoping part or barrel. These rings are adjacent the open annulus end and function as a snubbing mechanism for reducing lateral flexing and vibrations between the telescoping members of the jar and as a result, these rings protect the fluid seals isolating the chamber containing the latching mechanism. For example, in the mentioned patent, the barrel 14 of the jar carries internally enlarged grooves 52 in which annular resilient elements 54 formed of rubber, neoprene or the like are disposed. The inner peripheries of these rings engage the mandrel 22 of the jar to resist lateral movement of the mandrel or barrel so as to protect the fluid seals adjacent to these rings. Additionally, it will be apparent that the annulus between the fluid seals or packing 34 and the annular rings 52 is segregated from the well bore. As a result, telescoping of the barrel and mandrel of the drilling jar greatly changes the liquid volume of this annulus. In order to prevent changes of volume in the annulus which would destroy the seals or the annular rings, openings 58 are provided so that there is fluid communication between the annulus and the surrounding well bore.
In most well drilling operations, the drilling fluid is a drilling mud which has thixotropic properties. These properties allow the drilling mud to be moved by a pump freely through the well bore. However, removal of the pumping force allows the mud to reach a quiessant or resting stage wherein its properties produce a gel or non-newtonian fluid state. Thus, it will be apparent that the segregated annulus between the packing and rings within the mentioned drilling jar is filled with a drilling fluid which is not exposed to circulating flow conditions. Thus, the drilling mud within the annulus of the drilling jar is in a gel stage. The telescoping of the barrel and mandrel of the drilling jar during impact delivery occurs relatively suddenly. However, there is a finite time required for the drilling mud to go from the gel state to its newtonian fluid state and flow between the annulus and the well bore. Thus, a severe piston effect can occur under certain jarring conditions when the drilling mud cannot flow through the mentioned openings 58 with sufficient rapidity to compensate for the fast changing volume of the annulus between the seals and packing. Therefore, the drilling mud by its incomprehensible volume can injure either the fluid seals or the annular rings for snubbing lateral movement or vibration between the barrel and mandrel of the drilling jar. This problem of fast varying annulus volume is common both to mechanical jars and also to other types of jars, such as employing hydraulic mechanisms for the cocking and releasing functions.
Another problem exists relative to the annular rings, such as the rings 52 of the U.S. Pat. No. 3,233,690, which are employed for dampening the lateral movements or vibrations occurring between the inner and outer members as the jar provides the impact function. At impact, large amounts of energy are applied to these members which produce lateral and longitudinal movements or vibrations, both of harmonic and nonharmonic variations. The annular dampening rings 52 of the jar shown in the mentioned patent have produced a remarkable longevity in protecting the fluid seals in the jar. Unfortunately, at infrequent intervals even these annular dampening rings failed to prevent the fluid seals from suffering distructive effects of these induced vibrations. One explanation for this severe effect is that the vibrations induced into the outer and inner telescoping members of the jar are not limited to transverse displacement but include both longitudinal and circular displacements and all variations of their combination. The vibrations induced between the telescoping members of the jar are especially severe when it is recognized that the inner and outer members of the jar in producing the desired impact forces upon the well drill string, in many cases, also rotate relative to one another. Thus, annular snubbing rings, such as employed in the past, can be placed into a failing mode whenever there is a combination of both axial and circular acting vibrations of great magnitude on the inner and outer members of the jar.
The present invention is a well tool in the nature of a rotary drilling jar which has unique resilient snubbers between the telescoping parts of the jar which are so arranged as to reduce the problem of longitudinal flexing and vibration induced injury either to the snubbers or to the fluid seals associated with these jars. In addition, the new snubbers provide fluid passageways which permit the ready flow of the drilling fluid between the well bore and the annulus between the snubbers and the fluid seals. In addition, the snubbers are of a unique design and can be employed with other types of well tool having telescoping members.